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Estimating Full IM240 Emissions from Partial Test Results: Evidence from Arizona


  • Ando, Amy
  • Harrington, Winston

    () (Resources for the Future)

  • McConnell, Virginia

    () (Resources for the Future)


The expense and inconvenience of enhanced vehicle emissions testing using the full 240-second dynamometer test has led states to search for ways to shorten the test process. In fact, all states that currently use the IM240 allow some type of fast-pass, usually as early in the test as second 31, and Arizona allows vehicles to fast-fail after second 93. While these shorter tests save states millions of dollars in inspection lanes and driver costs, there is a loss in information since test results are no longer comparable across vehicles. This paper presents a methodology for estimating full 240 second results from partial-test results for three pollutants: HC, CO and NOx. Using random sample of vehicles in Arizona which received full 240 second tests, we use regression analysis to estimate the relationship between emissions at second 240 and emissions at earlier seconds in the test. We examine the influence of other variables such as age, model-year group, and the pollution level itself on this relationship. We then use the estimated coefficients in several applications. First, we attempt to shed light on the frequent assertion that the results of the dynamometer test provide guidance for vehicle repair of failing vehicles. Using a probit analysis, we find that the probability that a failing vehicle will passing the test on the first retest is greater the longer the test has progressed. Second, we test the accuracy of our estimates for forecasting fleet emissions from partial test emissions results in Arizona. We find that forecast fleet average emissions are very close to the actual fleet averages.

Suggested Citation

  • Ando, Amy & Harrington, Winston & McConnell, Virginia, 1998. "Estimating Full IM240 Emissions from Partial Test Results: Evidence from Arizona," Discussion Papers dp-98-24, Resources For the Future.
  • Handle: RePEc:rff:dpaper:dp-98-24

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    References listed on IDEAS

    1. Small, K.A. & Kazimi, C., 1994. "On the Costs of Air Pollution from Motor Vehicules," Papers 94-95-3, California Irvine - School of Social Sciences.
    2. Alberini, Anna & Harrington, Winston & McConnell, Virginia, 1996. "Estimating an Emissions Supply Function from Accelerated Vehicle Retirement Programs," The Review of Economics and Statistics, MIT Press, vol. 78(2), pages 251-265, May.
    3. Charles F. Manski & Ephraim Goldin, 1983. "An Econometric Analysis of Automobile Scrappage," Transportation Science, INFORMS, vol. 17(4), pages 365-375, November.
    4. Kazimi, Camilla, 1997. "Evaluating the Environmental Impact of Alternative-Fuel Vehicles," Journal of Environmental Economics and Management, Elsevier, vol. 33(2), pages 163-185, June.
    5. Parks, Richard W, 1977. "Determinants of Scrapping Rates for Postwar Vintage Automobiles," Econometrica, Econometric Society, vol. 45(5), pages 1099-1115, July.
    6. Robert W. Hahn, 1995. "An Economic Analysis of Scrappage," RAND Journal of Economics, The RAND Corporation, vol. 26(2), pages 222-242, Summer.
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    Cited by:

    1. Ando, Amy & Harrington, Winston & McConnell, Virginia, 1999. "Costs, Emissions Reductions and Vehicle Repair: Evidence from Arizona," Discussion Papers dp-99-23-rev, Resources For the Future.
    2. Ando, Amy & Harrington, Winston & McConnell, Virginia D., 2007. "Fees in an Imperfect World: An Application to Motor Vehicle Emissions," Discussion Papers dp-07-34, Resources For the Future.

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